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Synthetic routes towards bioinspired composites

A. R. Studart Complex Materials, Department of Materials, ETH Zurich

The intricate hierarchical organization of biological materials like bone, teeth and plants finds no counterparts within man-made composites. Implementation of such nano-/microstructural design in synthetic composites should enable the creation of materials with unusual combination of properties and functionalities. Despite ongoing efforts to understand the complex cell-mediated processes that lead to such hierarchical architectures, mimicking synthetically the structural organization of natural materials remains a major challenge. An alternative approach is to devise new directed assembly routes to organize colloidal building blocks into bioinspired structures in the absence of cellular control. In this talk, I will present some of our recent attempts to develop such directed assembly routes and how we can utilize them to translating biological design principles into new materials and devices. First, I will show a new approach to obtain polymer-based composites exhibiting deliberate orientation of reinforcing particles using ultra-low magnetic fields. The ability to control the position and orientation of reinforcing particles within a polymer matrix leads to bioinspired heterogeneous structures with unusual out-of-plane stiffness, wear resistance and shape-memory effects. In the second part of the talk, I will show that an elastomeric polyurethane matrix can be hierarchically reinforced with nano- and microplatelets to form hybrid materials with local elastic modulus varying up to five orders of magnitude. Inspired by the tendon-to-bone interface in skeletal tissues, we control the local reinforcement level of the polymer to create polymeric substrates that can be stretched several times its initial length, while keeping the local strain on specific surface sites lower than 1%. The unusual mechanical properties achieved in these examples illustrate the great potential of this bioinspired approach in creating synthetic composites with rich functional behavior using a limited set of building blocks.